diff --git a/README.md b/README.md
index ce9f2b1..fb35a47 100644
--- a/README.md
+++ b/README.md
@@ -11,7 +11,8 @@ Method names and functionalities are inspired by [Kotlin.Collections](https://ko
 
 ### 1.1 Notes
 
-* This extension requires PHP 7.1 and above.
+* Requires PHP 7.1 and above.
+* Currently not working on MacOS. Fix in progress.
 
 ## 2. Documentation
 
diff --git a/src/collections_methods.c b/src/collections_methods.c
index d69d23a..cc98a33 100644
--- a/src/collections_methods.c
+++ b/src/collections_methods.c
@@ -1009,7 +1009,7 @@ PHP_METHOD(Collection, last)
         RETURN_NULL();
     if (EX_NUM_ARGS() == 0) {
         HashPosition pos = current->nNumUsed;
-        while (pos >= 0 && Z_ISUNDEF(current->arData[pos].val))
+        while (pos <= current->nNumUsed && Z_ISUNDEF(current->arData[pos].val))
             --pos;
         RETURN_ZVAL(&current->arData[pos].val, 1, 0);
     }